One example of liquid crystal display devices is disclosed in Japanese Patent No. 2,837,027 (published on Dec. 14, 1998, corresponding U.S. Pat. No. 5,402,255).
FIGS. 18, 19 and 20 illustrate how input/output signals are exchanged between driver ICs in the conventional liquid crystal display device. For example, driver ICs are usually connected via a substrate (Printed Wired Board, PWB) as illustrated in FIG. 20.
FIG. 18 illustrates a TCP of the conventional driver IC. An input/output signal external connection terminal section 51, which is commonly used by a plurality of driver ICs, is provided on a lower side (on the side opposite to a liquid crystal drive output external connection terminal section 55 is provided) of the TCP (Tape Carrier Package). The input/output signal external connection terminal section 51 and connection lead terminals of PWBs 71, 72 and 75 are connected by soldering. In this way, the connection for the input/output signals is realized between the driver ICs.
The TCP includes (i) a driver chip 57 substantially at the center, (ii) the liquid crystal drive output external connection terminal section 55 at the upper side, (iii) the input/output signal external connection terminal section 51 (commonly used by a plurality of driver ICs) at the lower side and (iv) terminals S1 to S7 which come out from the lower side.
The chip portion is covered with a resin so as to be protected electrically and physically. Generally, the liquid crystal drive output external connection terminal section 55 is connected to the liquid crystal panel via an anisotropic conductive sheet. On the input/output signal external connection terminal section 51, slits are formed by cutting out the TCP. Then, by connecting the input/output signal external connection terminal section 51 with PWB, it becomes possible to commonly supply a signal to a plurality of driver ICs.
FIG. 19 is an enlarged view of a portion where the driver chip 57 is connected with the TCP. Pads 67 on the driver chip 57 and inner leads 64 at the center of the TCP are thermo-compression-bonded with each other, so as to be electrically and physically connected with each other.
In this arrangement, the terminals S1 to S7 of the input/output signal external connection terminal section 51 are provided so that one terminal corresponds to one signal. Naturally, one pad corresponds to one signal.
FIG. 20 is a diagram illustrating an arrangement of a conventional liquid crystal module. Assuming that the liquid crystal panel illustrated in FIG. 20 is a 640 (transverse direction)×480 (longitudinal direction) dot panel, each of eight source drivers (four at an upper side, and another four at a lower side) have 160 outputs for driving liquid crystal, and each of four common drivers provided on a left side have 120 outputs for driving liquid crystal.
The following description explains a basic principle of how the liquid crystal is driven by the liquid crystal driving device in reference to FIGS. 21 to 24. FIG. 21 is a diagram illustrating a basic principle of how the liquid crystal is driven. Liquid crystal deteriorates when an electric field is continuously applied thereto in one direction for a long period of time, because of its electrochemical property. Therefore, as illustrated in FIGS. 21(a) and 21(b), it is necessary to reverse, from period to period, the direction of the electric field applied to the liquid crystal.
In addition to the above inversion driving per period, there is an inversion driving per dot of a panel as a method of applying the electric field to a liquid crystal panel. FIGS. 22(a) to 24(b) illustrate various methods of the inversion driving. ● and ∘ are dots to each of which the electric field is applied, but the directions thereof are opposite to each other. Each of FIGS. 21(a), 22(a) and 23(a) illustrates a state in a certain vertical period, and each of FIGS. 21(b), 22(b) and 23(b) illustrates a state in the following vertical period. FIGS. 22(a) and 22(b) illustrate a case in which all the dots are inverted at the same time per frame. FIGS. 23(a) and 23(b) illustrate a case in which the dots are inverted per line in a display perpendicular direction (line inversion driving), and the dot are also inverted per frame. FIGS. 24(a) and 24(b) illustrate a case in which, in addition to the case of FIG. 23, the dots are inverted per dot in a horizontal direction (dot inversion driving).
The above cases are different from each other in ease of building a display system and in image quality. The driving method of FIG. 24 can produce images with the highest quality. The driving method of FIG. 24 is disclosed, for example, in International Publication WO96/06421 (published on Feb. 29, 1996).
FIG. 25 is a block diagram illustrating an arrangement of a driving device, which adopts the dot inversion driving of FIG. 24 disclosed in International Publication WO96/06421.
In the driving device adopting the dot inversion driving, a plurality of operational amplifiers 76 are provided. To an output terminal of each of the operational amplifiers 76, two switching elements 102 and 104 are connected. These two switching elements 102 and 104 are formed by the first and second MOS transistors, respectively. Drain terminals 96 of the switching elements 102 and 104 are connected to a load capacitance C2.
A gate terminal of the first switching element 102 is coupled with a SELECT signal, and a gate terminal of the second switching element 104 is coupled with a complementary SELECT signal (an inversion signal of the SELECT signal).
A source terminal of the first switching element 102 is coupled with an external memory capacitor 66, and a source terminal 65 of the second switching element 104 is coupled with an output of the operational amplifier 76. When the SELECT signal is high, the switching element 102 is turned on, and the switching element 104 is turned off. When the SELECT signal is low, the switching element 102 is turned off, and the switching element 104 is turned on.
The external memory capacitor is provided for carrying out a charge sharing. The charge sharing is one type of precharging. That is, by utilizing the electric charge remaining in the source signal lines in a certain horizontal period, the precharging of the source signal lines is carried out in the following horizontal periods. As for the precharging, before the potential of the source signal line is set to the source signal potential for the horizontal period, a voltage is applied to the source signal line in advance. An object of this voltage application is to cause the source signal line to reach a desired source signal potential as quickly as possible.
In FIG. 25, a value of the external memory capacitor 66 is selected so that the value of the external memory capacitor 66 is much larger than N times of the value of the load capacitance C2. Note that, N is the number of source signal lines in an arrangement of pixels, and C2 is the load capacitance typically connected with one source signal line in the arrangement of pixels. During the first portion of the horizontal period, the electric charge accumulated on the load capacitance C2 is discharged to the external memory capacitor 66. The external memory capacitor 66 acts as a large-size electric charge sink. In the line inversion driving, each source driver needs to apply high and low voltages alternately in each horizontal period.
In the line inversion driving, voltages are not randomly applied (that is, the applied voltage is not unknown in each horizontal period), but polarities of the voltages regularly shift in the horizontal period. On this account, energy for switching a load capacitance to be high is used for switching a next load capacitance to be low. Therefore, it is possible to decrease a voltage newly applied at the beginning of the horizontal period.
Adversely, energy for switching a load capacitance to be low is used for switching a next load capacitance to be high. Therefore, it is possible to decrease a voltage newly applied at the beginning of the horizontal period.
The external memory capacitor 66 time-averages voltages applied to the source signal lines. In the line inversion driving, an average voltage charged on the external memory capacitor 66 is a bias voltage between a maximum positive voltage and a minimum negative voltage (whose absolute value is maximum) applied to the source signal line. For example, when the maximum positive voltage is 6 V and the minimum negative voltage is −6 V, the bias voltage is 0 V. Therefore, the external memory capacitor is 0 V or close to 0 V.
The external memory capacitor 66 is connected between a common line (not illustrate) and a bias voltage source which is at a ground potential in this case.
In the driving device illustrated in FIG. 25, when the SELECT signal is high, the switching element is turned on, and the switching element 104 is turned off.
Therefore, when the SELECT signal is high, a plurality of switching elements 102 are turned on at the same time, and are connected to the external memory capacitor 66 provided externally. The external memory capacitor 66 then carries out the charge sharing so that the electric power charged to the load capacitance 96 from the output of the operational amplifier 76 is collected or discharged to the external memory capacitor 66.
Liquid crystal display devices have been developed in order to meet the demand of increasing the size of the screen for use in TVs, PCs, etc. Moreover, mid-size and small-size liquid crystal display devices and liquid crystal driving devices are developed for use in mobile terminals, such as mobile phones which are rapidly expanding its market in recent years.
For the screens of the liquid crystal display devices used for the above purposes, the liquid crystal driving devices are strongly desired to be small, be light, support many outputs, be high in speed, be low in cost, be high in display quality, and be low in power consumption (including a case of battery-driven).
However, because the number of pixels and the materials are different between a newly designed liquid crystal panel and a conventional liquid crystal panel, load capacitances and the like are also different between them, and hence external memory capacitors required for adequately carrying out the charge sharing are also different between them. On this account, in order to obtain the effect equivalent to that of the charge sharing of the conventional liquid crystal display device by using the newly designed liquid crystal display device, it is necessary, in the conventional technology, to adjust the timing of the pulse width (high period) of SELECT signal outputted from a controller so that an outputted driving voltage temporarily gets close to a medium driving voltage. For this, it becomes necessary to arrange a new controller.